Since beta-amyloid is a putative causal agent for Alzheimer's disease (AD), we have examined some of its effects on ion transport across cell membranes. Incubation of PC-12 cells with beta-amyloid for 24 hours caused a significant increase in the choline conductance of the cells. If a similar effect occurs in cholinergic neurons of AD patients, the leakage of choline out of the neurons could reduce the intracellular concentration of choline and result in decreased synthesis and secretion of acetylcholine. This could explain the reduced concentration of acetylcholine in the brains of AD patients.